Time compression and expansion recording system



Nov. 5, 1968 A. LIBERMAN 3,409,144

TIME COMPRESSION AND EXPANSION RECORDING SYSTEM Filed Aug. 14. 1964REVERSIBLE VARIABLE SPEED MO TOR /7 AMPLIFIER mvE/v TOR.

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3,409,744 TIME COMPRESSION AND EXPANSION RECORDING SYSTEM Arie Liberman,Skokie, Ill. Talk-A-Phone Company,

5013 N. Kedzie Ave., Chicago, Ill. 60625) Continuation-impart ofapplication Ser. No. 14,242, Mar. 11, 1960. This application Aug. 14,1964, Ser. No. 389,703

1 Claim. (Cl. 179-1002) ABSTRACT OF THE DISCLOSURE This invention isconcerned with an improved recording system particularly designed forrecording or reproducing a selection in a time different from that inwhich it was originally performed.

This application is a continuation-in-part of my copending applicationSer. No. 14,242, filed Mar. 11, 1960, noW abandoned.

It is sometimes desirable to reproduce a selection, as a musical work,in a time different from that in which it was initially performed. Forexample, musical selections are quite often played from a recording Overcommercial radio stations which have a rather inflexible programmingschedule into which musical selections do not fit. As a result,selections are usually cut to fit the time available or a portion of thebroadcast time filled with other material of questionable interest.

A principal object of this invention is the provision of a system forcompressing or expanding a selection without altering either the contentor the frequencies involved, but only changing the tempo or speed atwhich the selection is rendered.

One feature of the invention is the provision of a system for varyingthe time of a recorded selection, comprising recording the selection,translating the recording at a rate different from the rate ofrecording, thereby shifting the frequencies thereof, and re-recordingthe selections at the shifted frequency. The re-recording is thenreproduced at a translating rate which shifts the frequencies to thoseof the original. However, the time of translation of the re-recordingdiffers from that of the original selection dependent upon thedifference in rate of the original recording and translation.

A further feature is the provision in a recording system of a firstrecording medium, a first recording device, a pickup device, means fordriving the recording medium in operative relation with the recordingand pickup devices, means for moving one of the devices with relation tothe recording medium, a second recording device connected with thepickup device, a second recording medium, and means for driving thesecond recording medium in operative relation with said second recordingdevice.

Yet another feature is that the recording medium is a magnetic tape andthe movable device is a generally round and elongated transducer with agap arranged transversely of the axis of the medium and in a generallyspiral configuration.

Still a further feature is the provision in a magnetic recording systemof a transducing device having Opposite ends with a generallycylindrical wall, with a magnetic tape tangent to the wall at atransducing point, and the United States Patent m 7 3,409,744 ICPatented Nov. 5, 1968 wall having a signaltransducing slot thereinextending from one end toward the other and completelyaround thecylindrical wall. And another feature is that a continuous loop ofmagnetic tape passes by both a record and a playback transducer, one ofwhich has a single helical slot and with which the tape is tangent alongan axial line, and the other of which-has a single slot thereinsubstantially at right angles to the tape.

Further features and advantages will readily be apparent from thefollowing specification and from the drawings, in which:

FIGURE 1 is a diagrammatic representation of a system embodying theinvention; n

FIGURE 2 is a diagrammatic illustration of a recording or pickuptransducer forming a part of the invention;

FIGURE 3 is a two dimensional pattern of the surface of the transducerof FIGURE 2;

FIGURE 4 is a diagrammatic illustration of a section of tape recorded inaccordance with the illustrated embodiment of the invention; and

FIGURE 5 is a fragmentary elevation illustrating the transducing slot ofthe pickup transducer.

Previously proposed methods for compressing or expanding the timerequired to perform a selection have required that the selection bedivided into small discrete elements, some of which are eliminated incompressing the selection and some of which are repeated in expandingthe selection. This type of operation is limited in the degree ofcompression or expansion which may be effected without losing fidelityor intelligence. This is particularly apparent where the selection isfirst compressed, eliminating a portion of the discrete elements thereofand then expanded, repeating some of the elements which were left. Theresulting selection may differ materially from the original. With thepresent novel method and system, nothing is lost or repeated, merely thetempo is changed, but without altering the frequencies.

The apparatus of this invention may be used to compress or expandrecorded radio and television programs to fit a specific time period.Certain programs as commercials might be recorded at a very slow tempoand then compressed to take a much shorter time without losing anyintelligence. Transient effects, as in electrical circuits, may beexpanded in time without altering their frequency composition to permitdetailed study and analysis.

Turning now to the drawings, a system embodying the invention is shownin FIGURE 1. An endless loop 10 of a recording medium, as a magnetictape material, extends past a recording transducer 11, pickup transducer12 and a capstan 13 operated by drive motor 14. An erasing head 15 isoperatively associated with the recording loop 10 between pickup andrecord transducers.

An amplifier 16 has input terminals 17 which may be connected with asuitable source, as the output of another record playing device, andoutput terminals 18 connected with record transducer 11. Pickup head 12is connected with second record head 20 operatively associated with asecond recording medium 21, shown as a magnetic tape extending betweentake-up and supply reels 22 and 23, respectively.

The record transducer 11 is specially designed with a recording gap orslot extending generally spirally or helically about the surfacethereof, as will appear below, to permit the head to be rotated withrespect to the tape while continuously impressing a signal thereon. Thetransducer is rotated by a reversible variable speed motor, indicateddiagrammatically at 27.

Briefly, the system operates as follows. With the tape 10 driven at aconstant speed, assume that recording transducer 11 is rotated in adirection opposite the direction of movement of the tape. This in effectincreases the recording rate, i.e. if the rate of movement of the tapeis 2 inches eral velocity of 1 inch per second in the oppositedirection,-

recording takes place at an effective rate of 3 inches per second.However, the recorded signals are translated by pickup transducer 12 atthe rate of travel of tape 10, 2 inches per second. As a result, thefrequencies of the selection at the pickup are lower than thoseinitially recorded.

The signal from pickup 12 is coupled to second record head 20 whichimpresses it on a second recording medium or tape 21, at the lowerfrequency. Of course, the recording time of the second recording mediumis the same as the original time for the selection. In order toreproduce the re-recorded signal at the original frequencies, recordingmedium 21 must be played at a rate different from that at which thesignals were recorded thereon. In this case, Where the frequenciesrecorded thereon are lower than the original frequencies, the tape mustbe played at a faster speed to return the signals to the originalfrequency, resulting in time compression or performance of the selectionin a time less than that required for the initial rendition.

Conversely, if record transducer 11 is rotated in the same direction asthe movement of tape 10, the effective recording rate is slower than thepickup rate at transducer 12 and the frequencies of the selection pickupare higher than the original frequencies. The re-recorded selection ontape 21 must be played more slowly than it was recorded, increasing thelength of time necessary to perform the selection.

FIGURE 2 illustrates one form of transducer 25 embodying the invention.Transducer 25 is generally cylindrical about an axis 25a and is providedwith a continuous spiral transducing gap 26 extending around thecylindrical wall from one end of the transducer to the other. In thediagrammatic representation of the transducer surface unrolled in FIGURE3, gap 26 is actually a straight line extending diagonally across thesurface. Spiral gap 26 has an angular extent of 360, one complete turnaround the cylindrical transducer. It is desirable that the anglebetween the gap and a line parallel with the axis of the transducer beno more than 60. The recording tape is held by a backup member 28 sothat it has substantially only a line contact with the surface of thetransducer. The stationary transducer 12 has a single straight gap 29,FIGURE 5.

If the recording transducer 11 is stationary, information is recorded ina narrow band along the length of the tape 10. If the recordingtransducer is rotated by motor 27, information is recorded in a seriesof narrow diagonal bands 31, as illustrated in FIGURE 4. The angle ofthe bands with respect to the longitudinal axis of tape depends on therelative speed of the tape and the periphery of the recordingtransducer. The direction of the diagonal bands depends on the directionof rotation of the transducer with respect to movement of the tape. Thedirection of magnetization of the tape is normal or at right angles tothe tangent to the slot or gap. As the pickup transducer 12 has a gap 29which is at right angles to the direction of movement of the tape 10, itis necessary that the angle of recording be limited, for properreproduction. If the angle between the helical gap 26 and the axis ofthe transducer is no greater than 60, satisfactory operation isachieved.

The operation of the system will now be analyzed in somewhat more detailwith the aid of the scalar quantities indicated in FIGURE 1 of thedrawing. It is assumed that the tape 10 is driven at a constant speed Vin the direction of the arrow indicated on the drawing, and that therecording transducer 11 is driven by reversible, variable speed motor 27with a peripheral or gap speedi-V the sign as indicated, positive whenthe direction of rotation is opposite the direction of movement of thetape and negative when in the same direction. The symbol f, representsthe frequency at record transducer 11, f the frequency at pickuptransducer 12 and V the speed of the second recording tape 21, duringrecord. The velocity of recorda and the recording head may be expressedas r= u i rh The speed of pickup, V i.e. the relative speed between thetape and pickup head 12, is V or may be expressed As the speed of pickupdiffers from the speed of record, the frequencies derived by pickup 12will differ from the original recorded frequencies according to therelationship Of course, as the playback speed differs from the recordingspeed, the playback time will also differ from the original time, andthis relationship may be expressed as a ratio 312 (vs) 1 tli rh Thisterm may be designated a time multiplier or simply TM.

The most common situation in utilizing this invention is that one willhave a selection with a given original running time and a desiredrunning time. The speed and direction of the transducer is unknown, butmay be expressed as rli T2 Thus, by merely setting the speed anddirection of record transducer 11 in accordance with the desired changein playing time, the tape velocities of T T and vtg may be selected oradjusted as desired, bearing in mind only the relationship of V and Vnecessary to return the re-recorded selection to the originalfrequencies.

The pickup head 12 may be made movable instead of the record head 11 andthe same general relationships between velocities, frequencies and timeare present.

While I have shown and described certain embodiments of my invention, itis to be understood that it is capable of many modifications. Changes,therefore, in the construction and arrangement may be made withoutdeparting from the spirit and scope of the invention as disclosed in theappended claim.

I claim:

1. A magnetic recording system for varying the duration of a selectionwithout altering the content or frequencies thereof, comprising: asource of signal representing the selection in its original form; acontinuous loop of magnetic recording tape; means for moving said tapepast two spaced signal transducing points at a velocity of V a recordingtransducer at one of said points and connectable with the source ofsignal to be recorded; a pickup transducer at the other of said pointsand having an output, said pickup transducer being fixed and having atransducing slot extending generally at right angles to the direction ofmovement of said tape, said recording transducer having opposite endswith a generally cylindrical wall, and a longitudinal axis, the tapebeing tangent to said wall and moving in a path generally at rightangles to the axis, said wall having a signal transducing slot extendingin a helix from one end to the other end and around said wall; means forrotating said cylindrical transducer about its longitudinal axis with avelocity V so that the signal is recorded in narrow diagonal bands onsaid tape; said rotating means including means for varying the speed ofrotation of said transducer and for reversing the direction of rotationthereof; and means for recording the output of said pickup transducer,reproduction of said last mentioned recording with a velocity tomaintain the frequencies of the original generating said selection inits entirety and in a time related to the original time of the selectionby a factor of References Cited UNITED STATES PATENTS 2,800,384 '7/1957Parker 179 100.2 2,875,436 2/1959 Hammond 178--6.6 2,886,650 5/1959Fairbanks et al. 179-1002 2,903,521 9/1959 Ellison 179 100.2 2,909,61610/1959 Marty 179 100.2 3,066,196 11/1962 Stern 179 100.2 3,077,5872/1963 Springer ..1791002 10 3,313,890 4/1967 Lopez 17'9 100.2

r millan Company, New York; 1958; pp. 377-386.

BERNARD KONICK, Primary Examiner.

I. R GOUDEAU, Assistant Examiner.

